The reaction of N-substituted 1-amino-3-alkylthio-2-propanols, synthesized from the C-2-C-5 natural mercaptan fraction, with aldehydes was investigated. 2,3-Disubstituted 5-alkylthiomethyloxazolidines were obtained as a result. 2-(beta-alkylthioethyl)-2-R"-, 2-(gamma-alkylthiopropyl)-2-methyl-3-R-oxazolidines and 2-(beta-alkylthioethyl)-2-methyl-3-R-5-alkylthiomethyloxazolidines were obtained by condensation of N-substituted beta-amino alcohols with beta- and gamma-alkylthioketones. They were tested as oxidation inhibitors for blended diesel fuels. Some of these compounds, added in small amounts to OMI industrial inhibitor, can significantly increase its effectiveness in thermal stabilization of this fuel.